The present invention relates to a device for switching a connection depending on the state of an apparatus to be monitored, especially a safety switch.
DE 196 24 172 A1 discloses a safety switch with an actuator which is mechanically polarized by its geometry. When inserted into a switch housing, the actuator turns a drum controller. Also, the safety switch has a transponder which, in the completely inserted state of the actuator, can be read out by a read/write device located in the switch housing.
EP 0870 653 discloses a belt lock. The position of a safety element, which secures the locking element of the belt tongue against unintentional spontaneous release and which is slidably movable, may be detected by means of a Hall probe and a magnet. In the event of manual actuation of the unlocking button of the belt lock, the safety element is displaced form its locking position.
DE 197 11 588 A1 discloses safety switches with an actuator which has a first signalling means fixed preferably on the apparatus to be monitored. The actuator can be brought together with an actuator receiver having a second signalling means, and can be removably blocked in it against pulling back. Between the first and the second signaling means, signal exchange can be done without contact. In the known safety switches, the actuator can be blocked in the united position by an axially movable plunger which fits through the opening of the actuator. Blocking or interlocking can be actuated both by spring force or magnetic force. In doing so, two pairs of signalling means which belong together are necessary in order first to detect the united state of the actuator and actuator receiver and second to detect the blocking state of the plunger.
Objects of the present invention are to provide a device which can be produced easily and economically, and still ensures permanently reliable holding closed and monitoring, in a wide variety of environments.
Only one pair of matched signalling means is necessary according to the present invention. If signals can be exchanged between these two signalling means, it is ensured that the actuator and the actuator receiver are brought together and blocked in this position. This arrangement is synonymous with the apparatus to be monitored, for example a safety means, such as a protective hood or a protective grating on a machine tool, being closed and secured in the closed state (closed and locked). In the course of bringing together the actuator and actuator receiver, their engagement to one another necessarily occurs, and thus, the position of blocking engagement is assumed. The signalling means are located on the actuator and actuator receiver such that only in the position of the blocking engagement is signal exchange possible. The matching signalling means can be made in different ways. For example, only one of the two signalling means can send a signal or information. The other signalling means issued essentially for complete or partial reflection of the emitted signal, for example, emission of light or ultrasound. Alternatively, the other signalling means can receive the emitted signal and send it back unchanged or individually changed to the signalling means. In doing so, analog and/or digital signals can be transmitted in one or both directions. Preferably, one of the signalling means also makes available energy for operation of the other signalling means in the form of electromagnetic radiation in the visible or invisible wavelength range. Signals can thus be exchanged without contact since the signals are not exchanged via electrical contacts, but can be transmitted wirelessly. Because the actuator is necessarily in blocking engagement with the actuator holder by their being brought together, a plunger that blocks the actuator can be omitted.
Because the actuator and actuator receiver have interworking blocking surfaces which are brought into blocking engagement with one another when the actuator and actuator receiver are brought together, and which block withdrawal of the actuator from the actuator receiver, self-locking is accomplished. In other words, the actuator is prevented from moving away from the actuator receiver, for example, due to vibration. The blocking surfaces can be made and/or aligned with respect to the insertion direction of the actuator such that the blocking forces increase when pulling on the actuator. The actuator can additionally be held by an energy storage mechanism or an electromagnet in the position of blocking engagement.
Because the blocking surfaces with the direction of motion of the actuator when bringing together include an angle from 0 to 90xc2x0, especially from 60 to 90xc2x0, self-locking is intensified and the blocking forces when pulling on the actuator are increased. Preferably, the blocking surfaces are made such that they hook into one another.
Because the first and second signalling means are located on the respective blocking surfaces and are opposite one another especially in the position of blocking engagement, it is ensured with especially simple means that signal exchange between the actuator and the actuator receiver is possible only in the position of blocking engagement of the actuator and the actuator receiver. Protection against false closing, i.e. protection against signal exchange although the actuator is still not yet blocked, is greatly increased.
Because the first and/or the second signalling means have a directional characteristic with at least one preferred spatial direction for signal exchange, protection against false closing is further increased since signal exchange is not possible when the two signal means approach. Only when the position of blocking engagement has been assumed and the two signalling means are directly adjacent, especially opposite, is the signal exchange possible.
Because the actuator can be swiveled, especially is fixed to be able to swivel on the apparatus to be monitored, it can be brought into blocking engagement with the generally stationary actuator receiver especially easily. The actuator can preferably be swivelled around an axis which includes a right angle with the insertion device or coincides with it. The actuator generally does not have its own power supply, i.e. the signalling means attached to it obtains its power, if necessary, from the electromagnetic field which has been built up by the second signalling means. Of course, in addition or alternatively, the actuator can also be movable. Also, the actuator receiver can be swivelled and/or movable.
Because the actuator assumes the position of blocking engagement when brought together with the actuator receiver as a result of the force due to its weight, an additional energy source for the blocking of the actuator is not necessary. If blocking is desirable or necessary in each installation position, in addition or alternatively, there can be blocking actuated by spring force or magnetic force.
Because signal exchange takes place electromagnetically, the safety and reliability of the device are further increased. Signal exchange can take place, for example, via electromagnetic waves or (ultra)sonic waves. In the case of electromagnetic waves, there is signal exchange by means of radio waves and by means of optical radiation. In both cases, energy transmission is also possible. In particular, signal exchange based on radio waves can be made available with standard components and thus economically. One signalling means transmitting the inquiry is received by the other signalling means and is sent back to the first signalling means unchanged or optionally individually changed. In this way, for example, detection and identification of the actuator are possible.
Because the blocking engagement is released as a result of electromagnetic force or by means of compressed air supply, opening, for example, a protective hood for a machine tool can be controlled by the control for the machine tool. Alternatively or in addition, release by means of a cable, for example a Bowden cable, is possible. The actuator and the actuator receiver can be made such that a one-time release pulse leads to motion out of the position of blocking engagement, and thus, to unblocking which enables subsequent and optionally time-staggered opening and removal of the actuator.
Other objects, advantages and salient features of the present invention will become apparent from the following detailed description, which, taken in conjunction with the annexed drawings, discloses preferred embodiments of the present invention.